Electromagnetic transducer with twisted wire core



March 29, 1966 J. PARSTORFER ELECTROMAGNETIC TRANSDUCER WITH TWISTED WIRE CORE Filed April 6. 1961 9 Sheets-Sheet 1 INVENTOR.

JOHN PARSTORFER /me wf,

AGENT March 29, 1966 J. PARsToRl-'ER 3,243,519

ELECTROMAGNETIC TRANSDUCER WITH TWISTED WIRE CORE Filed April e, 1961 9 sheets-sheet zy INVENTOR.

JOHN PARSTORFER AGENT March 29, 1966 J. PARsToRFr-:R 3,243,519

ELECTROMAGNETIC TRANSDUCER WITH TWISTED WIRE CORE Filed April G, 1961 INVENTOR.

JOHN PARSTORFER AGENT March 29, 1966 J. PARsToRFER ELECTROMAGNETIC TRANSDUCER WITH TWISTED WIRE CORE 9 Sheets-Sheet 4 Filed April 6. y1961 INVENTOR JOHN PARSTORFER AGENT March 29, 1966 J. PARsroRFER 3,243,519

` ELECTROMAGNETIC TRANSDUCER WITH TWISTED WIRE CORE Filed April 6. 1961 9 Sheets-Sheet 5 NVENTOR JQHN PARSTORFER IIII AGENT March 29, 1966 J. PARSTORFER ELEcTRoMAGNETxo TRANsDUcER wml TWISTED WIRE com Filed April e. 1961 9 Sheets-Sheet 6 NVENTOR JOHN PARSTORFER AGENT March 29, 1966 J. PARsToRFER ELECTROMAGNETIC TRANSDUCER WITH TWISTED WIRE CORE Filed April e, 1961 |36 l 24 */176 Zo INVENTOR.

JOHN PARSTORFER AGENT March 29, 1966 J. PARsTQRl-ER ELECTROMAGNETIC TRANSDUCER WITH TWISTED WIRE CORE Filed April G. 1961 9 Sheets-Sheet 9 INVENTOR. JOHN PARsToRFER AGENT United States Patent O 3,243,519 ELECTROMAGNETIC TRANSDUCER WITH TWISTED WIRE CORE John Parstorfer, Philadelphia, Pa., assignor to Burroughs Corporation, Detroit, Mich., a corporation of Michigan Filed Apr. 6, 1961, Ser. No. 101,292 4 Claims. (Cl. 179-1002) The present invention relates genenally to electromagnetic transducer apparatus, and to electromagnetic transducers which have improved operating characteristics at extremely high frequencies. More particularly, it is concerned with electromagnetic transducer construction wherein plural information may be recorded and/ or picked up from a plurality of independent closely spaced data tracks on a record member by means of a unitary multichannel electromagnetic transducer assembly.

With still more particularity, the present invention is concerned with certain fabrication techniques for producing individual electromagnetic transducers capable of operating in the foregoing manner by providing a read-record |head structure which is adapted to read or write information on record media such, for example, as tapes, drums or discs. In addition, the present invention is concerned with a novel multichannel electromagnetic transducer assemlbly including a plurality of read-record heads in which each head may be made in extremely small sizes `and at less expense than analogous heads known heretolfore, and which effect a greater economy of magnetic materials than has been the case in the past. `In this latter respect the present invention is further concerned with novel manufacturing techniques which result in greater accuracy of alignment of the several structural portions comprising the head, as well as in a greater facility in the handling of smaller bodies of magnetizalble or magnetic material.

It is an important object therefore of the present invention to provide an improved magnetic transducer.

Another object of the present invention resides in the construction of novel multichannel magnetic transducer assemblies.

A further object of the present invention resides in the provision of novel manufacturing techniques for the construction and hermetic encapsulation of small electromagneticv read-write heads, either singly or in multiples.

In accordance with the foregoing objects and first briefly described, the present invention comprises in one of its important aspect-s an electromagnetic transducer wherein a plurality of magnetizaible elements are secured together into a bundle, axially twisted one or more times throughout their length, provided wtih a plurality of turns of electrical conductors which are distributed therealong, circularly bent to bring the ends into parallel abutting arrangement with a shim of non-magnetic material disposed in the gap therebetween, after which the ends are fastened together and the assemlbly is hermetically encapsulated to form a sealed miniature electromagnetic transducer assemhly.

In accordance with the foregoing objects, the present invention also comprises in another of its aspects a multichannel electromagnetic transducer assembly foaming a stick or recording bar of electromagnetic transducers disposed in a row.

In another of its aspects the invention comprises an as sembly of parallel rows of electromagnetic transducers wherein the transducers of one row have their operating gaps offset from the operating lgaps of the next adjacent parallel row whereby the center-to-center spacing fbetween the gaps of the various rows of transducers may be relatively small, on the order of .050 inch, thus to provide inice terlaced sensing of the inform-ation from a record memher.

Another important aspect of the invention is the provision of a novel method of manufacture or fabrication of individual electromagnetic transducers.

The foregoing objects and advantages, construction and operation of the present invention will become more readily apparent from the following description and accompanying drawings in which:

FIG. l represents a portion of a 'bundle of electrical conductors for use with the present invention;

FIG. 2 is an end view of the bundle of conductors of FIG. 1;

FIG. 3 represents an end view of a bundle of conductors having a square cross-sectional configuration;

FIG. 4 is a plan view o-f a clamping and supporting ribbon for use with the present invention;

FIG. 5 is a view illustrating the manner in which the conductors are overlayed on the supporting ri'blbon;

FIG. 6 is a view illustrating the manner in which the holding members of the supporting ribbon are clamped over the bundle of conductors and shows the individual segments which are removed therefrom;

FIG. 7 is a View of one of the segments of FIG. 6;

FIG. 8 is a view of the supporting ribbon of FIG. 7 with the excess material removed;

FIG. 9 is a view along line 9 9 of FIG. 8;

FIG. 10 is an isometric view of a twisting and winding apparatus for the present invention;

IFIG. 11 is a front elevational view of the apparatus of FIG. 10 as used during a twisting operation;

FIG. 12 is a view across the line 12-l12 of FIG. l1;

FIG. 13 is a view similar to FIG. 11 but showing the apparatus as used during a winding operation;

FIG. 14 is a sectional view along the line 14-l14 of FIG. 13;

FIG. l5 is a view showing the manner in which the bundle of conductors is twisted or wound by the apparatus of FIG. 10;

FIG. 16 is a view showing the manner in which the energizing windings are applied to the conductors forming the core of the transducer;

FIGS. 17 and 18 are vie-ws illustrating the manner in which the bundle of conductors is end formed;

FIG. 19 is an isometric view of a holding and forming jig or fixture for use with the present invention;

FIG. 20 is a detail view of an air gap shim;

FIGS. 2l and 22 are views illustrating the use of the jig of FIG. 19;

FIG. 23 is an enlarged sectional view of one end of an assembled transducer;

FIG. 24 is an exploded view of an encapsulating jig for the present apparatus;

IFIG. 25 is a sectional View of the assem-bly of FIG. 24;

FIG. 26 is a sectional View taken along the line 2-6 216 of FIG. 25;

lFIG. 27 is a sectional View of the jig of FIG. 24 with a transducer disposed therein for encapsulation;

'FIG. 28 is a front elevational view, partially in section, along the line 28-28 of FIG. 27;

FIGS. 29 and 30 are views of a transducer before and after the excess shim and pin conductor stock is removed;

FIG. 31 is a view of the transducer with the energizing leads attached thereto;

IFIG. 32 is a view of the gap end of the device of FIG. 31;

\FIG. 33 is a plan view of a portion of a multi-channel transducer assernbly or stick; and,

|FIG. 34 is a sectional view along the line 34-34 of F-IG. 33.

formed thereby.

Referring now to FIGS. 1 through 9, which will be described conjointly in detail, there is seen a plurality of magnetizable elements, such as insulated magnetic wires 10, which are brought together into parallel, side by side arrangement to form a fiat bundle or group 12 with each element lying closely adjacent, i.e., touching each adjacent conductor. The configuration shown in FIG. 1 includes six elements, however, the number of elements is a vmatter of choice, depending ron the size, e.g., diameter of the individual elements and the ultimate over-all size of the individual transducer assembly which is to be In the present preferred embodiment this bundle or group 12 of magnetizable wires may be of molypermalloy annealed 1material and may be stretched out longitudinally for several feet, flat and parallel, touching side by 'side as before mentioned. Oxide'insulation around each wire is desirable to give lamination etfects. The diameter of such magnetic wire is approximately .002 to :006 inch, FIG. 2. The wire may also be squareshaped as seen in FIG. '3. K

A clamping and/or 'supporting ribbon 14 etched, punched, or otherwise preformed, out of .001 or .O02 inch brassor Iother similar shim stock material is provided, 1ncluding elongated parallel portions 16 having transverse, parallel pairs `of cross members 18 `extending therebetween 'and located -at regular intervals lthroughout its' length. From a central por-tion 20 interconnecting `each pair of transverse cross members 18, sets of double spikes 22 project in opposite directions away therefrom. the number of clamping spikes can be chosen to suit the convenience of the design and may be more or less than that illustrated herein.

The clamping ribbon 14 may be placed. beneath the core forming bundle 12 or conversely, the bundle 12 may be laid over top of the shim stock 14, parallel to the portions 1620 as seen in FIG. 5. The spikes 22 are then crimped over the wires 10, as indicated by reference character 24 in FIG. 6, and may, if desired, be adhered thereto as by a ldrop of liquid cement 26, FIG. 9, for example. One section 28 at a time may then cut along the cutting lines 30-30, FIG. 6, and is separated from the assembly as seen in FIG. 7.

The proper .and/ or desired assembly length :is provided by the prefixed distance between adjacent pairs or sets of parallel cross members :1S- 18. Obviously, t-his length may be varied -to fit the particular 'size `of the transducer assembly which is to result therefrom. The upper and lower parallel portions lr6-16 are then clipped olf `along the cutting lines 32--32 (.FIG. 7) producing the open assembly of F-IG. '8. T'he vertically disposed cross pieces 18 remain-for easier handling and support as well as to prevent or lessen skewing of the individual magnet wires during `clamping in the handling `apparatus to be described in detail hereinafter.

Referring now to FIGS. 1`0 through .14, vthere is shown a coil wind-ing and wire twisting apparatus 36 for use in further fabrication of the transducer of the present invention. The core Winder 36 comprises a base or frame 38 from which a pair of vertically disposed supporting pedestals 40-42 project. .'Eachpedest-alis drilled, FIGS. 11-l3, to receive the respective opposite shaft ends 44 and 46 of `a cylindrical or barrel-like `gear `member 48. A spring 50 slidably received in an 4elongated aperture 52 in pedestal 42 biases the gear member 48 leftwardly, FIGS. ll and L13, whereby the barrel gear is transversely slidable left and right. The opposite shaft end 44 of the barrel gear 48 terminatcs in anfenlarged collarv54 integral with a'drive wheel `56having a handle 58 projecting therefrom for hand rotation thereof for purposes to be disclosed hereinafter. Disposed immediately behind the pedestals 40 and 42, and projecting also upwardly away from the base 38 is `a sec- -ond set of pedestals 60 and-62, in which shafts '64 and 66 are journalled in a known fashion.

A rotatable toothed gear wheel 68 is mounted on shaft 64 for rotation therewith. The -teeth 70 of gear 68 are in mesh lwith the teeth 72 of the drum or barrel gear 48. A toothed gear wheel 74 mounted on shaft 66 yfor rotation therewith also has its teeth 76 in mesh with the teeth 72 of gear y48. Shafts |64 and 66 are each provided with an axial bore 78-78 (FIG. 12) throughout their respective lengths for purposes to be explained hereinafter. Pedestal 62 is provided w-ith a set screw 80 normally holding gear 714 fixed. When this screw is loosened however, gear 74 may then be manually slidably, Aadjustable relative to the gear 48 so as to vary the spacing between the two gears 68 and 74 permitting, among `other things, varying length transducer assemblies -to be accommodated thereby.

Each gear 68 and '7-4 is provided with an adjustable chuck or jaw-like arrangement 82, FIG. 14, on -its exposed face. Each chuck V82 includes a fixed block 84 secured as by screws 86 to the face of a respective `gear 68 and 74. A movable vjaw element 88 is adjustable relative to block 84 by means of bolts 90-90.

In order that gear 68 maybe -fixed or rotatable at will relative to barrel gear 48 a lock or detent 92 is provided therefor. Detent 92 includes an elongated plunger ymember A94, the enlarged end portion 96 Aof Ywhich is knur'led thus to provide handling means therefor. `Plunger 94 is slidably movable back and forth against the tension "of a coiled spring 98, within 'the bore 100 of the receptacle yor chamber 102. A collar "104 ofjplunger 94 retains the spr-ing .98 within the receptacle 102. The projecting end 105 of plunger 94 'is receivable ywithin 'a depression or recess .106, FIGS. v1l and '13, in the side of gear 68 and when engaged therewith holds the gear 68 in a fixed position. A latch 108 on plunger 94 permits the plunger lend to be held in a retracted position out of the recess 106, as seen in FIG. 13, so that either one or bothgears -68 and 74 can engage gear 48 .as desired.

`Located directly behind the second pair of pedestals 60 and 62 is a vertically disposed post 110, FIGS. l0 and 14. A detachably mounted rotatable wrespool 112, carrying a supply of conductive wire 114, has lits shaft 11.6 journalled for rotation in the upper end .of the post 110. A -knurled latch 118, FIG. 10, on the end `of .the shaft 11'6, permits the supply spool to be hand rotated and/or removed at will. A resilient, flexible member 120, secured by screws 122 to the post 110, is angled `over the spool rims so as to press thereagainst and in this manner apply .tension to the coiled wirev 114 on spool 112 thus preventing accidental withdrawal or unwinding thereof.

The .post is `pivota-lly mounted at its .bottom portion on a cross shaft 124 .press tted at its opposite ends in blocks 126-126 which are attached .to the:base 38, FIG. l0. The rearwardly facing bottom :edge 128 of the .post 110 is arcuately chamfered as yshown in FIG. 14, so that the post may be rocked from its full to its broken line position, FIG. l0, for maintenance or change of supply spool, etc. The post 110 .is transversely slidable along the shaft 1 24 Vleft to right and return, FIGS. 10, ll and 13, and carries a vfurther wire feeding tensioning, guiding and distrrbuting means provided by a pair 'of relatively thin, flat, elongated, parallelly disposed .members 1311-130 of suitable flexible material so as not to scratch or otherwise abraid the insulation as the wire is kmoved therebetween. The members 1311-130 of plastic, .for example, are :secured, as by screws 182 to `the post 110 and .are angled slightly away therefrom and over the bundle 12 of wires, FIG. .14. 'Phe foregoing 4construction permits the `wire 114 to be -distributively payed :out .away .from tth'e supply spool 112.

Returning again to the fabrication of the transducer assembly, the bundle of wires 12, as seen in FIG. 8, is now lplaced in the winding apparatus `3.6, FIG. E10, so that the bound ends 24 project slightly into and lbetween .the lfaces of blocks `84 and 88 of the chuck 82 in the manner shown in FIG. 12. Thereafter the vbolts 90-90 are tightened on each chuck so `as to securely retain the ends V24---24 of the Wire bundle 12 therebetween. Detent 92 Vis released so that plunger .1041s engaged in the recess `106 ofthe gear 68 holding the latter fixed, FIG. 11. The hand wheel 56 is pushed rightwardly, FIG. 11, against the tension of spring 50, sliding gear 48 out of engagement with gear 68. Thereafter the hand wheel is-rotated so as to twist the wire bundle 12 approximately two complete revolutions about itself, as indicated by reference character 134, FIG. 15, with just a slight amount of over travel in `order to offset the spring back effect as the Wires relax after the ends are removed later on from the jig 36. This twisting operation yguarantees that the ends 2'4-24 of the bundle will remain parallel to each other so that the wires continue in the same direction at each end after the twisting is accomplished. The wires are twisted as a convenience in handling and forming them into a circular shape, to be described hereinafter, without making extra provisions for such shape.

Additionally, the twisting operation produces a desirable and usefulV cancelling effectrelative to the stresses and the strain concentrations whichbuild up by virtue of the fact that the individual wires in the bundle effectively change position` from inside to outside along the curve ofthe circle asthe bundle is circularly bent in the manner hereinafter described.

An induction coil 136, providing an energizing winding for applying a current or voltage level to the transducer assembly, may be wound therearound in the manner hereinafter describedviDetent 92 is moved leftwardly, FIG.*-13, and memberV 96'rotated slightly to lock plunger 104`out of engagement with' gear 68. Barrelgear 48 is then movedleftwardly under urging by spring 50, FIG. 14, thereby engaging its teeth 72 with both gears 68 and 74.l Pose" 110, FIG. 14, is in its broken line position, FIG. 10. 'l A leader or short length of wire 114 is then withdrawn `from* the spool 112 and passed between the guidesr130-130 and its end either is secured to the bundle 12 or the end may be passed once around the bundle 12 and temporarily hand held.

By means of the knurled knob 118 the supply spool 112 is lrotated counterclockwise so as to move the post 11-0 intothe vertical position, FIG. 14, during which movement of the wire guides 130-130 approach and pivotally rest firmly but lightly against the twisted wire bundle 134. This tensioning means provides an even pull on the wire 114 and since the parallel guides 130-130 ride right over the wire bundle while distributing the coils therealong, the bundle cannot bow or deform axially throughout its length as i-t might otherwise do without such means. Also the foregoing arrangement permits each coil t-o be laid evenly adjacent each other coil during the lback and forth movement of the post 110 in distributing the windings turns of wire 114. Wheel 56 is then rotated mechanically or by hand so as to apply winding turns of wire 114 thereto. As the wire 114 is unwound and payed away from the spool 112, the post 110 is manually slid back and forth along the shaft 124. The tensioning member 120 pressed against the rims of the spool of wire prevents the wire from being accidentally released from the spool and provides additional tension thereon so that the wire is tightly applied around the transducer wire bundle 12.

By means of the wire feeding and distributing apparatus just described, approximately one to two hundred turns of wire, loosely spaced and in several layers (FIG. 16) is wound around the core forming wire bundle 12. The Winding turns may constitute either the read and/ or write induction coilv or both, as the case may be. This induction Winding aids in retaining the wires in a tightly compacted bundle without other external support or xtures and it also prevents the wires from flattening out as they would normally tend to do after the bending procedure next to be described.

After the windings have been applied, the portions 18-18 of the cross bars are bent outwardly (FIG. 16) awayvfrom the central core body, from the full to the broken line positions y(FIGS. 16-18) and the remainder 6 is pressed back upon itself (FIG. 18). severed along the cutting line 13S-138.

The core forming assembly is then circularly bent into a substantially horseshoe shape by means now to be described, so that its fiat pole-forming ends 24-24 may be positioned parallel to one another. For these purposes, a -transducer bending and forming jig or fixture 140, FIG. 19, is seen to comprise a base 142 from which projects a central vertically disposed cylindrical member or rod 144. The upper end of rod 144 is undercut to provide a shoulder or ledge 146 and is further provided with a transverse slot 148 extending axially downwardly from the end 150 and some distance below the shoulder 146. An upper and a lower disc 152 and 154, respectively, are mounted over the rod 144 via apertures 156. Each disc has a set screw 158 for adjusting the angular position of the discs relative to each other and to the rod 144. An arcuate slot 160 is provided in each disc adjacent the central aperture 156. Each disc carries a vertically disposed post 162 and 164 respectively. Post 164 is made fast to the top disc 152, while post 162 is secured to the bottom disc 154 and extends vertically upwardly through the arcuate slot 160 in disc 152. From the foregoing it may be seen that movement of the set screws toward one another in the direction of the arrows 1'6 6- 166 will cause the discs to rotate in opposite directions to bring the two posts 162 and 164 together in substantially abutting relation-the post 162 moving freely in slot 16d-for purposes to be explained presently. As will be pointed out hereinafter, a pair of wire terminal attachment members 167--167 may be slip-fitted into holes 16S- 168 in upper disc 152 for employment later on in the fabrication of the transducer assembly.

The assembly of FIG. 16 is now bent slightly arcuately by hand and then located over the member 144, FIG. 21, so as to seat or rest upon the shoulder146 with the ends 24--24 ex-tending horizontally away from the member 144. A non-magnetic spacing shim 170, FIG. 20, of substantially rectangular shape and formed with a central projection or tab 172, is located in the slot 148 with the ftab disposed in the air gap or space between the confronting ends 24-24 as seen in FIGS. 21 and 22. The shim may be of any suitable non-magnetic material, such for example, as silver or copper, etc.

The discs 152 and 154 are then rotated in opposite directions, as before described, to bring the two pins 162 and 164 together thereby causing the ends 24-24 to be drawn tightly against the opposite sides ofthe spacing shim 170. The ends 24-24 `are then bound t-o the shim as by wrapping the excess metal tabs 18-18 in reverse directions therearound, FIG. 22, thus producing a constant and even pressure against the pole ends 24--24. This construction results in an end configuration as seen in FIG. 23. The free ends 174174 of the induction coil 136 are then attached in suitable fashion, as by soldering, to the earlier mentioned removable terminal forming conductors or pins 167-167 vertically disposed in the Iholes 16S-168 in the upper disc 152. The transducer assembly is now ready to be hermetically encapsulated, as will next be described.

As seen most clearly in FIGS. 24 through28, which Will be discussed simultaneously, an encapsulation molding jig or xture 176 for the present invention includes three main sub-assemblies including mating blocks 178 and 180 which are adapted to be secured together by means of bolts 182-182, and a cap or cover member 184 which is attached by bolts 186 to the other two members.

The cover member 184 is provided on its lower surface with a shallow central cut-out or recess 188, the parallel opposite edges 190-190 of which are adapted to slightly overlap the vertical wall portions 192492 of the assemblies 178 and 180, respectively, FIG. 25, in this manner provide a close and tight lit between all three members when they are assembled together. Ingress apertures 194-194 for reception therethrough of the potting or The material is encapsulating `material `are drilled or otherwise formed in the cover 184 for communication with the other two assemblies 178 and l180.

For purposes to be explained presently, the upper edges of each of the members 178 .and 180 are provided with opposite parallel shoulders or ledges 198-198 and 198'- 198 respectively.

Located between the openings 194-194 in the cover 184 are two parallel holes or depressions 20u-260, FIG. 25, forming receptacles into which the terminal for-ming and positioning members 167-167 are receivable so as to further strengthen and rigidify the transducer during the encapsulation thereof. Each of the central body forming portions 178 and 180 of the assembly is provided with a stepped chamber 202 and 204 cut or formed as an image of the external configuration of the transducer assembly. Oppositely disposed wing portions '20d-206 open outwardly away therefrom and form angled Ichannels interconnecting Vthe holes 194 therewith. The central portion of each chamber 202 and 204 is flanked by a flat :rectangular depression 208-203 respectively, into which the shim 1710 is receivable thus providing means for further orienting, locating and fixedly maintaining the transducer assembly within the jig 176.

Oppositel'y disposed apertures 210-210 in respective blocks 170 and 130, axially aligned with the holes 200- 200 in cover '184, Vpermit the lower port-ions of terminal pins 1'67-167 to align therein further rigidifying the assembly for final encapsulation.

With jig '17!6 i-n assembled condition, FIGS. .2S-28, the transducer .assembly is disposed therein as seen in FIGS. -2'7 and 28 with the opposite sides of the shim 170 received within the slot provided therefor and with the pins 167-167 located in the `.upper and lower holes 200 and 210-21'0' respectively.

Encapsulating material 212, FIGS. 29-34, `such as epoxy resin of suitable viscosity may now vbe poured through the openings 11.94 `to flow downwardly over the 4slanted floor of wings 206-206 so as to surround and enclose and thoroughly encompass the transducer assembly.

The apertures 200--200` in the cover 184 when the :lat-ter isassembled :together with members 176 and 178 provide relief areas Within which ambient air is trapped. \When the encapsulating .material `is poured into the mold- 4ing jig the `trapped 'air effectively blocks the molding material below ythe level of the central body portion of the cover and thereby prevents it from. touching or contaminating the upper ends of the members 167-167. Once cleaned and made ready Afor soldering, etc., the members 167-167 vremain free of yany local debris or contamination.

After the encapsulating material has hardened sufliciently, .the mold may be broken at its junctures `by removing the bolts and separating the .parts from each other exposing the transducer to view, as seen in FIG. 29. Thereafter, the excess shim stock is removed, FIG. y30,

and -the lower portion 213 of the transducer, including the members -24--24 which were wrapped around the bundle of Wires to hold the same together, are cut off, `FIG. 31, to form a -at surface portion 214 which, in the nal assembly, becomes the operating end of the he-ad, 4as seen most clearly in FIG. 32.

As beforementioned, each recording head may be disposed in side by side relationship with other similar heads in a -single or in -a double row, as shown for example, in FIGS. 3'3 and 34. In order to insulate each 'transducer `from its adjacent vcontiguous neighbor, a dielectric `element 216 is or lmay be introduced between each pair Vof transducers in the stick assembly 218. In 'this manner any magnetic-electric interaction between the various heads may be held to a minimum and the structure further `rigidiied thereby. It is noted that the operating gaps 220 of one row of heads are offset or ldisplaced slight-ly with respect to the operating gaps 4220 of the adjacent parallel row of heads. The plurality of heads may be cast or molded in the frame or stick 218 in FIG. 33. This arrangement is merely suggestive of a manner in which the apparatus may be used. Other and different arrangements may be chosen to suit specific applications. Nevertheless, the arrangement hereinbefore described will operate efficiently at .001 or .050 in centerto-center track spacing. The recording head stick or frame 218 may be used as a reading or writing assembly, or both alternately. The recording frame is ruggedly constructed giving long lasting reliable performance.

The present invention, as hereinbefore described, is useful, for example, in recording information on or `reading information from a disc, tape or drum-type memory storage unit (not shown). The techniques set forth are adaptable to produce an extremely small size electromagnetic transducer assembly wherein each read-record head on the order of .250 x .250 x .100 inches. The individual transducer resulting from lsuch techniques is especially suitable for use where extremely high sensitivity, high resolution and high frequency operation, up to approximately ve megacycles per second is required, or desirable. As beforementioned, a plurality of vsuch transducers may be grouped together in parallel side by side relation to form. ya .recording bar, gang or stick. These bars or sticks may also be placed in side by side parallel arrangement with :other similar bars, sticks, etc. to form compacted group assemblies so that reading and/ or writing may be performed in an interlaced fashion with respect to the data tracks on the storage media, e.g., recording disc, tape or drum. Such recording tracks are or may be spaced at .10() inch or respectively at .050 inch centers thus considerably increasing the memory capacity by virtue of the increase in packing ,density of the transducer-forming elements of the assembly.

The present vinvention lends itself very well to anelectrical circuit arrangement wherein the energizing windings for the various transducers in the stick assembly 218 could be in series or in parallel or both as fdesired. For example, in operating the stick wit-h a magne-tizable tape it might be desirable and/ or more efficient to employ a series arrangement for different operational functions such as erasing, writing and recording. Regardless vof the design the present transducer assembly is completely adaptable and operates equally ecient in all three situations.

The foregoing progressive production procedures permit the manufacture of uniformly constructed electromagnetic transducers with substantially identical characteristics from one to another. The process is applicable for hand or automatic assembly techniques and the method is basically simple, thus resulting in lowering manufacturing costs for miniature-type recording heads to an economical price range.

What is claimed is:

1. An electromagnetic transducer for reading o-r record-v ing high frequency magnetic information respectively `from or on a tape, disc or drum comprising:

(a) a bundle of continuous, discrete, similar lengt-l1 insulated wires of magnetic material having the mid portions thereof twisted upon one another for at least once about their long axes,

(b) said bundle of wire elements being bent into a toroidal `shape with the opposite end portions brought together in parallel spaced confronting arrangement so that these portions are adjacent to but slightly spaced from each other to form a pole gap therebetween,

(c) non-magnetic spacer means filling said pole gap,

(d) electrically conductive wire wrapped around the twisted mid-portion of said bundle .of elements forming an inductive electrical signal input-output assembly therewith, and p (e) electrical connector means attached to the ends 0f Sad electrically conductive signal assembly and extending away therefrom for interconnection to a utilization device whereby said transducer may function to either read or record.

2. An electromagnetic transducer for reading or recording high frequency magnetic information respectively from lor upon a tape, drum or disc, comprising:

(a) a bundle of continuous, discrete, similar length insulated wire elements of magnetic material having the mid porti-ons thereof twisted upon one another through .an arc of at least 360 about their long axes,

(b) said wire elements being bent into a horse-shoe shape with 1the opposite end portions brought together in parallel, straight, confronting arrangement so that these end portions are adjacent to but slightly spaced from each other to form a pole gap therebetween,

(c) non-magnetic metallic spacer means lling said pole gap,

(d) winding turns of electrically conductive wire encircling the twisted -mid portions of said magnetic wire elements forming an inductive electrical signal input-output a-ssembly therewith,

(e) .means hermetically encapsulating the transducer to form a sealed assembly, and

(f) electrical connector means attached to the ends of said electrically conductive input-ou-tput assembly and extending externally of said encapsulating means for interconnection to a utilization device whereby said transducer may function to either read or record.

3. An electromagnetic transducer assembly for reading or recording magnetic data respectively from or upon a tape, drum or disc including a plurality of individual transducer members each of which comprises:

(a) a bundle of continuous, discrete, elongated wirelik-e magnetic elements disposed in side by side arrangement,

(b) said bundle being axially twisted about itself throughout the major part of its length leaving the wire-like elements of each end of the bund-le untwisted and extending parallel to one another in a single plane,

(c) an induction coil for said transducer having input .and outputs ends, said coil being overlaid on said twisted part of said bundle of wire-like elements so as to extend approximately the full length of this part of the bundle, said bundle being bent into the general shape of a horseshoe having the opposite untwisted ends brought together so that the respective planes of the wire-like elements thereof extend radially of the horseshoe shape and in close parallel proximity to one another and con-timing lthe lines of magnetic ilux into an extremely small, well-defined area forming an air gap,

(d) a non-magnetic spacing shim disposed in the air gap between the planes of said opposite ends of the -bundle so -that the magnetic ux lines are obliged to bridge the very small area between the ends of the bundle as defined by the air gap,

(e) means mounting said transducer-s in side by side -parallel relationship, and

(f) dielectric means hermetically sealing said assembly of transducer .members from the atmosphere but providing electrical communication of the input and -output ends of the coil externally lof thevdielectric sealing means for operative -association with a utilization device.

4. An electromagnetic transducer assembly for reading or recording high frequency magnetic information respectively from or upon a tape, disc or drum comprising:

(a) a bundle of continuous, discrete, elongated wirelike magnetic elements disposed in tightly packed single row side by side arrangement,

(b) sai-d bundle being axially twisted about itself throughout the major part of its length leaving the ends thereof untwisted,

(c) an induction coil for said rtransducer having input and output ends, said coil being overlaid on said twisted part of said bundle of wire-like elements so as to extend approximately the full length Iof this part of said bundle, said bundle being bent into horseshoe shape bringing the opposite -ends of said bundle together in close parallel proximity, so as to conne the line-s of magnetic flux into an extreme-ly small, Well-defined area forming an air gap,

(d) a non-magnetic spacing shim disposed between said opposite ends within said air gap so that the magnetic flux lines are obliged to bridge the very small area between the ends of the bundles as defined by the air gap, and

(e) dielectric means hermetically seal-ing said assembly from the atmosphere but providing electrical communication of the input and output ends of the coil externally of the dielectric sealing means for operative association with a utilization device.

References Cited by the Examiner UNITED STATES PATENTS 2,668,878 2/1954 Munroe 179-1002 2,674,031 4/1954 Buh-rendort` 29-155.57 2,674,659 4/1954 Bufhrendorf 179-1002 2,676,392 4/1954 Buhr-endorf 29-l55.58 2,677,019 4/1954 Buhrendorf 179-1002 2,702,833 2/1955 Ca-mras 179-1002 2,839,613 6/1958 Greene 179-1002 2,895,014 7/1959 Johnson 179-1002 3,005,879 10/1961 Moehring 179-1002 FOREIGN PATENTS 424,765 2/ 1935 Great Britain.

BERNARD KONICK, Primary Examiner. ELI J. SAX, Examiner.

IRVING L. SRAGOW, D. G. REDINBAUGH, Assistant Examiners. 

1. AN ELECTROMAGNETIC TRANSDUCER FOR READING OR RECORDING HIGH FREQUENCY MAGNETIC INFORMATION RESPECTIVELY FROM OR ON A TAPE, DISC OR DRUM COMPRISING: (A) A BUNDLE OF CONTINUOUS, DISCRETE, SIMILAR LENGTH INSULATED WIRES OF MAGNETIC MATERIAL HAVING THE MID PORTIONS THEREOF TWISTED UPON ONE ANOTHER FOR AT LEAST ONCE ABOUT THEIR LONG AXES, (B) SAID BUNDLE OF WIRE ELEMENTS BEING BENT INTO A TOROIDAL SHAPE WITH THE OPPOSITE END PORTIONS BROUGHT TOGETHER IN PARALLEL SPACED CONFIGURATING ARRANGEMENT SO THAT THESE PORTIONS ARE ADJACENT TO BUT SLIGHTLY SPACED FROM EACH OTHER TO FORM A POLE GAP THEREBETWEEN, (C) NON-MAGNETIC SPACER MEANS FILLING POLE GAP, (D) ELECTRICALLY CONDUCTIVE WIRE WRAPPED AROUND THE TWISTED MID-PORTION OF SAID BUNDLE OF ELEMENTS FORMING AN INDUCTIVE ELECTRICAL SIGNAL INPUT-OUTPUT ASSEMBLY THEREWITH, AND (E) ELECTRICAL CONNECTOR MEANS ATTACHED TO THE ENDS OF SAID ELECTRICALLY CONDUCTIVE SIGNAL ASSEMBLY AND EXTENDING AWAY THEREFROM FOR INTERCONNECTION TO A UTILIZATION DEVICE WHEREBY SAID TRANSDUCER MAY FUNCTION TO EITHER READ OR RECORD. 